The invention relates to a process for introducing a hardening sulfuric acid electrolyte into battery cells at a sulfuric acid density of between 1.20 and 1.31, using a water-in-oil emulsion with a polymer as a polyelectrolyte in the water phase, preferably with a polymer or copolymer of an acrylamide, the emulsion together with a sulfuric acid/silica mixture being inverted to give an oil-in-water emulsion which ten hardens.
German Offenlegungsschrift No. 3,539,834 discloses a similar process, wherein three components are used, viz., sulfuric acid, silica and a polymer polyelectrolyte emulsion. Silica is a pulverulent solid and is mixed with the sulfuric acid. The emulsion is then added. Thus, there are two liquid components, namely the mixture of sulfuric acid with silica, and the emulsion.
The use of a water-in-oil emulsion, which is subsequently inverted to give an oil-in-water emulsion, has the advantage that, because of the intervening inversion step, sufficient time is available for the transfer from the liquid phase into the hardened phase, so that the electrolyte can be filled into the battery cells in the thickened but still liquid state and hardened only after the end of the intervening inversion step.
However, when this process is used in practice, there is the disadvantage that the sulfuric acid/silica mixture required as the starting component quickly hardens itself, so that its storage life is relatively short. In fact, the mixture will harden to such a high viscosity after 30 to 90 minutes that the filling of the battery will no longer be possible.
There presently exists a need for a method of introducing a hardening sulfuric acid electrolyte into battery cells which will enable the separate components to be mixed thoroughly, wherein each component will have a relatively long shelf life prior to mixing.